Use of maleated styrene-ethylene-butylene-styrene triblock polymer for improved adhesion

ABSTRACT

There is disclosed a method for adhering rubber to reinforcing materials which comprises embedding a textile fiber or metal reinforcing material in a vulcanizable rubber composition comprising rubber, a vulcanizing agent, reinforcement, a methylene donor, a methylene acceptor and a maleic anhydride functionalized triblock copolymer having polystyrene endblocks and poly-(ethylene/butylene) midblocks.

This is a Divisional of application Ser. No. 08/636,620, filed on Apr.23, 1996, which is a Divisional of application Ser. No. 08/348,641,filed on Dec. 2, 1994, which is now U.S. Pat. No. 5,536,774.

BACKGROUND

It has been conventional practice to prepare various textile reinforcingfibers to be used in contact with rubber formulations by pretreatingthem with a mixture of a rubber latex and a phenol-formaldehyde resin inwhich the phenol has almost always been resorcinol. This is theso-called "RFL" (resorcinol-formaldehyde-latex) method. Another methodcommonly used is to generate the resin in situ (in the vulcanizedrubber/textile matrix) by incorporating in the rubber a formaldehyde (ormethylene) donor compound, for example, hexamethylenetetramine orhexamethoxymethylmelamine and a formaldehyde (or methylene) acceptorcompound, for example, a dihydroxybenzene compound such as resorcinol.The in situ method has been found to be particularly effective where thereinforcing material is brass-coated steel wire since pretreatment ofthe wire with the RFL system has been observed to be largelyineffective.

The in situ formed resins have been observed to enhance adhesion betweenthe rubber and the reinforcing material. This enhancement of adhesion isby a mechanism that is not completely understood. The in situ methodwhich entails compounding a vulcanizable rubber stock with thephenol-formaldehyde components is known in the art. The most commonlyemployed methylene acceptor is resorcinol, while the more commonlyemployed methylene donors are the N-substituted oxymethylmelamines. Theresin is formed in situ during vulcanization of the rubber creating abond between the fiber and the rubber irrespective of whether the fiberhas been pretreated or not.

The rubber industry utilizes resorcinol in conjunction with methylenedonors to form resins which are used in rubber compounds to enhancefilamentary reinforcement and to improve the physical properties,including aged physical properties, or tires and other compounded rubberformulations. These resins, whether preformed or formed in situ, canincrease the dynamic rubber stiffness, tire treadwear, interfacialadhesion and fabric adhesion to the rubber compound; while desirablymaintaining the values of and hopefully reducing the rolling resistanceand heat buildup of a tire.

With the constant demand on quality, producers of reinforcedvulcanizates are under pressure to produce more products able towithstand greater fatigue and longer-term service. Therefore, anyachievements in improving the interfacial adhesion between thereinforcement and rubber environment is needed.

SUMMARY OF THE INVENTION

The present relates to enhancing the adhesion of rubber to reinforcingmaterials through the use of maleic anhydride functionalized triblockcopolymer having polystyrene endblocks and poly-(ethylene/butylene)midblocks.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a method for adhering rubber to reinforcing materialswhich comprises embedding a textile fiber or metal reinforcing materialin a vulcanizable rubber composition comprising rubber, a vulcanizingagent, reinforcement, a methylene donor, a methylene acceptor and maleicanhydride functionalized triblock copolymer having polystyrene endblocksand poly-(ethylene/butylene) midblocks.

In addition, there is disclosed a vulcanizable rubber compositioncomprising rubber, a vulcanizing agent, reinforcement, a methylenedonor, a methylene acceptor and maleic anhydride functionalized triblockcopolymer having polystyrene endblocks and poly-(ethylene/butylene)midblocks.

One key aspect of the present invention is the use of a maleic anhydridefunctionalized triblock copolymer having polystyrene endblocks andpoly-(ethylene/butylene) midblocks. A functionality of from 1 to 5percent by weight as bound maleic anhydride may be used. Preferably, afunctionality of 1 to 2 percent by weight is used. One example of suchcopolymer is commercially available from Shell Chemical Company underthe designation Kraton® FG1901X. This material has a specific gravity of0.91 g/cc, a polymeric styrene content of 28 percent by weight, afunctionality of 2 percent by weight as bound maleic anhydride, a ShoreA Hardness of 75, a tensile strength (ASTM D412) of 5000 and anelongation at break of 500 (ASTM D412). The maleic anhydridefunctionalized triblock copolymer may be present in an amount rangingfrom about 1 to 50 parts by weight per 100 parts by weight of rubber(hereinafter referred to herein as phr). For purposes of thisdisclosure, the triblock copolymer is not to be considered as a rubberwhen calculating phr in the overall vulcanizable rubber composition.Preferably, the amount of triblock copolymer ranges from 5 to 20 phr.

Suitable rubbers which may be used in the present invention includenatural rubber, polybutadiene, cis-1,4-polyisoprene, polychloroprene,acrylonitrile-butadiene copolymers, butadiene-styrene copolymers,ethylene-propylene copolymers, ethylene-propylene-diene terpolymers,polyepichlorohydrin terpolymers, acrylic and fluoroelastomers,unsaturated and saturated block polymers and blends thereof. Thepreferred rubbers are natural rubber, polybutadiene,cis-1,4-polyisoprene, acrylonitrile-butadiene copolymers andbutadiene-styrene copolymers.

Another feature to the present invention is the use of a vulcanizingagent. Examples of suitable vulcanizing agents include elemental sulfur(free sulfur) or sulfur donating vulcanizing agents. Representativesulfur donating vulcanizing agents are amine disulfides, polymericpolysulfides and sulfur olefin adducts. Preferably, the vulcanizingagent is elemental sulfur. Vulcanizing agents are used in an amountranging from about 0.5 to 8 phr, with a range of from 1.0 to 3.0 phrbeing preferred.

The rubber compositions containing the maleic anhydride functionalizedtriblock copolymer contain a methylene donor. The term "methylene donor"is intended to mean a compound capable of reacting with the methyleneacceptor and generate a resin in-situ. Examples of methylene donorswhich are suitable for use in the present invention includehexamethylene tetramine, hexaethoxymethylmelamine,hexamethoxymethylmelamine, lauryloxymethylpyridinium chloride,ethyoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, thehydroxyl groups of which may be esterified or partly esterified, andpolymers of formaldehyde such as paraformaldehyde. In addition, themethylene donors may be N-substituted oxymethylmelamines, of the generalformula: ##STR1## wherein X is an alkyl having from 1 to 8 carbon atoms,R¹, R², R³, R⁴ and R⁵ are individually selected from the groupconsisting of hydrogen, an alkyl having from 1 to 8 carbon atoms, thegroup--CH₂ OX or their condensation products. Specific methylene donorsinclude hexakis-(methoxymethyl)melamine,N,N',N"-trimethyl/N,N',N"-trimethylolmelamine, hexamethylolmelamine,N,N',N"-dimethylolmelamine, N-methylolmelamine, N,N'-dimethylolmelamine,N,N',N"-tributyl-N,N',N"-trimethylol-melamine. The N-methylolderivatives of melamine are prepared by known methods. The amount ofmethylene donor that is used may vary. For example, amounts ranging from0.5 to 10 phr may be used. Preferably, from 1 phr to 3 phr is used.

In addition to the methylene donor, a methylene acceptor is used. Arepresentative example of methylene acceptor is resorcinol. The amountof methylene acceptor that is used may vary. For example, amountsranging from 0.5 to 10 phr may be used. Preferably, from 1 phr to 3 phris used.

The weight ratio of methylene donor to methylene acceptor may vary.Generally speaking, the weight ratio will range from 1:10 to 10:1.Preferably, the weight ratio ranges from 1:3 to 3:1.

The present invention may be used with conventional textile fiber ormetal reinforcing materials. Representative materials includepolyamides, Kevlar®, polyester, carbon fiber and metallic cords andmonofilaments. Such materials may be in the form of chopped fibers orcontinuous construction.

In addition to the above, other rubber additives may also beincorporated in the rubber. The additives commonly used in rubbervulcanizates are, for example, carbon black, tackifier resins,processing aids, antidegradants, fatty acids, activators, waxes oils andpeptizing agents. By class, representative of the conventionalantioxidants and antiozonants (commonly classified together asantidegradants) which may be used include monophenols, bisphenols,thiobisphenols, thioalkylphenols, polyphenols, hydroquinone derivatives,phosphates, thioesters, naphthylamines, diphenylamines and otherdiarylamine derivatives, para-phenylenediamines and quinolines. Typicaladditions of carbon black comprise about 20 to 100 parts by weight ofdiene rubber (phr), which for many tire applications is generally fromabout 40 to 70 phr. Typical additions of tackifier resins comprise about2 to 10 phr. Typical amounts of processing aids comprise about 1 to 8phr. Typical amounts of antioxidants comprise 1 to about 5 phr. Typicalamounts of antiozonants comprise 1 to about 5 phr. Typical amounts offatty acids such as stearic acid, oleic acid and the like comprise fromabout 1 to about 2 phr. Typical amounts of zinc oxide comprise 3 to 5phr. Typical amounts of waxes comprise 1 to 5 phr. Typical amounts ofprocessing oils comprise 5 to 50 phr. Typical amounts of peptizerscomprise 0.1 to 1 phr.

Accelerators are generally used in rubber compositions to control thetime and/or temperature required for vulcanization and to improve theproperties of the vulcanizate. In some cases, a single acceleratorsystem is used; i.e., primary accelerator. Conventionally, a primaryaccelerator i used in amounts ranging from about 0.5 to 2.0 phr. In manyother cases, combinations of two or more accelerators are used which mayconsist of a primary accelerator which is generally used in the largeramount (0.5 to 2.0 phr), and a secondary accelerator which is generallyused in smaller amounts (0.05-0.50 phr) in order to activate and toimprove the properties of the vulcanizate. Combinations of theseaccelerators have been known to produce a synergistic effect of thefinal properties and are somewhat better than those produced by use ofeither accelerator alone. In addition, delayed action accelerators maybe used which are not affected by normal processing temperatures butproduce satisfactory cures at ordinary vulcanization temperatures.Suitable types of accelerators that may be used include amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. Preferably, the primary accelerator is asulfenamide. If a secondary accelerator is used, the secondaryaccelerator is preferably a guanidine, dithiocarbamate or thiuramcompound.

Vulcanization of the rubber compound of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. Preferably, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air or in a salt bath.

The rubber composition containing reinforcing materials find utility in,for example, tires, motor mounts, rubber bushings, power belts, printingrolls, rubber shoe heels and soles, rubber floor tiles, caster wheels,elastomer seals and gaskets, conveyor belt, wringers, hard rubberbattery cases, automobile floor mats, mud flaps for trucks, ball millliners and the like. Preferably, the rubber compositions containing thereinforcing materials are used in tire applications including for use inbelts, sidewalls, carcasses, apex and chafers.

The following examples are provided for illustrative purposes and shouldnot be considered as limiting the scope of the invention. The parts andpercentages are by weight unless otherwise indicated.

EXAMPLE 1

Adhesion was evaluated using the Tire Cord Adhesion Test (TCAT). Sampleswere prepared and tested according to the procedures described by D WNicholson, D I Livingston and G S Fielding-Russell, Tire Science andTechnology (1978) 6, 114; G S Fielding-Russell and D I Livingston,Rubber Chemistry and Technology (1980) 53, 950; and R L Rongone, D WNicholson and R E Payne, U.S. Pat. No. 4,095,465 (Jun. 20, 1978).

Table I shows the ingredients used in this example. In addition,conventional amounts of carbon black, zinc oxide, processing oil,sulfenamide accelerator and guanidine accelerator were used. The rubbercompound was prepared in a two-stage procedure using a Banbury® mixer.The adhesion tests were conducted with polyester cord. All parts andpercentages are by weight unless otherwise noted.

                  TABLE I                                                         ______________________________________                                        Rubber Compound Used in Adhesion Tests                                        Material             Parts by Weight                                          ______________________________________                                        Polybutadiene.sup.1  17.50                                                    Emulsion SBR.sup.2   41.25                                                    (30 phr of SBR and 11.25 phr of oil)                                          Natural Rubber       52.50                                                    Resorcinol           1.00                                                     Hexamethoxymethyl Melamine (Active)                                                                1.00                                                     Sulfur               2.25                                                     Maleic Anhydride Functionalized                                                                    Varied                                                   Triblock Copolymer.sup.3                                                      ______________________________________                                         .sup.1 Budene ® 1207 commercially available for The Goodyear Tire &       Rubber Company                                                                .sup.2 PFL 1712C commercially available for The Goodyear Tire & Rubber        Company                                                                       .sup.3 Kraton ® FG 1901X                                             

The stress strain data for the samples were obtained using indicatedcure parameters as set out in Table II below along with the adhesiondata.

                  TABLE II                                                        ______________________________________                                                   Sample 1                                                                      Control  Sample 2 Sample 3                                         ______________________________________                                        Kraton ® FG 1901X                                                                      0          7.5      15.0                                         Pull Force.sup.1 (Neutons)                                                                 139        159      183                                          100% Modulus.sup.2 (MPa)                                                                   1.550      1.630    1.710                                        300% Modulus (MPa)                                                                         7.670      7.490    7.190                                        Tensile (MPa)                                                                              13.78      11.95    12.05                                        Elongation at Break (%)                                                                    486        459      492                                          ______________________________________                                         .sup.1 36 minutes at 150° C.                                           .sup.2 55 minutes at 175° C.                                      

It can be seen that Samples 2 and 3 have modulus values similar to thecontrol; however, they have a drastically higher pull-out force (cordadhesion).

What is claimed is:
 1. A method for adhering rubber to reinforcingmaterials which comprises embedding a textile fiber or metal reinforcingmaterial in a vulcanizable rubber composition comprising rubber, avulcanizing agent, reinforcement, a methylene donor, a methyleneacceptor and a maleic anhydride functionalized triblock copolymer havingpolystyrene endblocks and poly-(ethylene/butylene) midblocks.
 2. Themethod of claim 1 wherein said vulcanizable rubber composition comprises100 parts by weight of rubber, from 0.5 to 8 phr of a vulcanizing agent,from 0.5 to 10 phr of a methylene donor, from 0.5 to 10 phr of amethylene acceptor, and from 1 to 50 phr of a maleic anhydridefunctionalized triblocks copolymer.
 3. The method of claim 1 whereinsaid rubber is selected from group consisting of natural rubber,polybutadiene, cis-1,4-polyisoprene, polychloroprene,acrylonitrile-butadiene copolymers, butadiene-styrene copolymers,ethylene-propylene copolymers, ethylene-propylene-diene terpolymers,polyepichlorohydrin terpolymers, acrylic and fluoroelastomers,unsaturated and saturated block polymers and blends thereof.
 4. Themethod of claim 1 wherein the methylene donor is selected from the groupconsisting of hexamethylenetetramine, hexamethoxymethylmelamine,lauryloxymethyl-pyridinium chloride, ethyloxymethylpryridinium chloride,trioxan hexamethylolmelamine and paraformaldehyde.
 5. The method ofclaim 1 wherein the methylene acceptor is resorcinol.
 6. The method ofclaim 1 wherein said maleic anhydride functionalized triblock copolymercontains 2 percent by weight of bound maleic anhydride and 28 percent byweight of polymeric styrene content.